Generally, in a control panel for mechanical equipment such as machine tools and the like, a push-button-type emergency stop switch is provided to emergency-stop mechanical equipment at the time of abnormal circumstances. In such a push-button-type switch, for example, Japanese patent application laying-open publication No. 2003-303527 (hereinafter referred to JP '527) discloses a switch equipped with a “safety-Potentials® structure”, which is a registered trademark of IDEC Corporation, such that contacts of the switch will not return to a contact state in the event that the switch is damaged.
As shown in FIGS. 1 and 2 of JP '527, the button housing 9 receiving the push button 5 includes the compression spring 55 that biases the cylindrical member 45 at the bottom of the push button 5 toward the switch case 3 in the downward direction and the compression spring 31 that is provided at the bottom of the interlocking member 23 coupled to the bottom of the cylindrical member 45 and that biases the interlocking member 23 below the switch case 3 in the downward direction.
In this case, due to resiliently repellent force of the compressive spring 55, the interlocking member 23 is biased downwardly via the cylindrical member 45, and due to resiliently repellent force of the compressive spring 31, the interlocking member 23 is biased downward. Thereby, the movable contact 21 is biased toward the side that the movable contact 21 opens relative to the fixed contact 17.
Through operation of the push button 5, as the movable contact 21 moves away from and opens relative to the fixed contact 17, the amount of deformation of respective compression springs 55, 31 decreases, and elastic energy of respective compression springs 55, 31 thus decreases. That is, elastic energy of respective compression springs 55, 31 after opening of the contacts is smaller than elastic energy of respective compression springs 55, 31 before opening of the contacts.
Therefore, according to the push-button-type switch shown in JP '527, even in the event that the switch is damaged, the contacts will not return to the contact state again thereby displaying “safety-Potentials® function” as a push button switch.
However, in the abovementioned structure of prior art, there needs to be provided a spring discretely from the contacts that biases the movable contact away from the fixed contact, and as a result it is disadvantageous that the number of components increases and thus a manufacturing and assembly cost increases.
The present invention has been made in view of these circumstances and its object is to provide an operation switch that can decrease the number of components to reduce a manufacturing and assembly cost.